Miniaturized mobile radio receiver with dipole antenna

ABSTRACT

The miniaturized mobile radio receiver has a straight dipole antenna whose wires run along the edge of the printed-circuit board(s) of the radio receiver and are connected at their outer ends to conductive areas. The conductive strips on the circuit board(s) which run parallel to the antenna constitute a resistive-capacitive shunt and are, therefore, open in the vicinity of the antenna base to block the flow of RF signals.

The present invention relates to a miniaturized mobile radio receiverand more particularly to a dipole antenna for such a receiver.

A miniaturized mobile radio receiver of this kind is disclosed in DE-GM67 52 498. To form a straight dipole, the radio receiver described thereincludes two lines running within a housing formed by two plasticshells. The shells are held together at their narrow sides by twoconductive caps which are connected as capacitive loads to the ends ofthe dipole wires.

Conductive strips of a printed-circuit board in the housing which runnear the dipole wires strongly interact with the latter, and conductivestrips extending from one half of the dipole to the other represent aresistive-capacitive shunt to the antenna. This increases the lossresistance and the equivalent capacitance of the antenna.

The object of the invention is to provide an improved miniaturizedmobile radio receiver.

This object is attained by the means set forth in claim 1. Furtheradvantageous aspects of the invention are apparent from the subclaims.

UK Patent Application 2 029 112 A discloses a television aerialconsisting of a housing containing a preamplifier and a half-wave dipolewhose elements are formed from strips of metal foil and carried on acardboard or similar base. Connected to the base of the antenna is acoaxial cable running to the preamplifier. Besides the strips of metalfoil, the board carries no conductive strips.

In the miniaturized radio receiver according to the invention, thedecrease in the effective height and in the efficiency of the antennadue to the adjacent conductive strips is reduced to such a point thatvery high receiver sensitivity is achieved.

An embodiment of the invention will now be explained in more detail withreference to the accompanying drawings, in which:

FIG. 1 is a highly simplified representation of the antenna and itsequivalent circuit diagram;

FIG. 2 is an equivalent circuit diagram of the antenna with conductivestrips opened to block the flow of RF signals, and

FIG. 3 is a perspective view of printed-circuit boards with an antenna.

FIG. 1a shows a printed-circuit board 1 of a miniaturized mobile radioreceiver (not shown). Conductive strips and components have been omittedto simplify the illustration. Wires 2 running along the edge of thecircuit board 1 form a straight dipole antenna. At the outer ends of thewires, capacitive loads are provided in the form of metallic areas 3.Between the wires and the areas on one side and the conductive strips ofthe circuit on the printed-circuit board 1 on the other side,capacitances C_(S) are created (two of them are shown symbolically)whose value depends, inter alia, on the distance between the wires 2 andthe conductive strips. If conductive strips extend from one half of thedipole to the other, the capacitances will act from one half of thedipole on the other.

FIG. 1b shows the influence of the capacitances C_(S) on the antenna.The capacitances C_(S) act beyond the base region of the antenna and,thus, represent a resistive-capacitive shunt. This greatly increases theloss resistance and the equivalent capacitance of the antenna.

FIG. 1c shows the equivalent circuit diagram of the antenna. A generatorwith the open-circuit voltage U_(O) is connected in series with a lossresistance R_(A) and an antenna capacitance C_(A). Connected across thisseries combination are the capacitances C_(S), which have been combinedinto a single capacitance, and a resistance R_(S). For the antenna load(not shown), this results in a capacitive voltage division which greatlyreduces the output voltage of the antenna, and the resistive componentR_(S) causes a loss.

To avoid the resistive-capacitive shunt, all conductive strips of theprinted-circuit board 1 are opened in the base region of the diple toblock radio-frequency (RF) signals. This RF separation is indicated inFIG. 1a by the broken line 4. In conductive strips extending beyond theline 4 and interconnecting highly resistive sources and loads, resistorsR of about 100K ohms are inserted at this point, and in conductivestrips interconnecting low-resistance sources and loads, resonantcircuits are inserted. The resistors must have low capacitance andinductance values.

In the equivalent circuit diagram of FIG. 2, a large resistance R and aresonant circuit of frequency F_(O) are present in the branch of thecapacitance C_(S) and the resistance R_(S). Now, almost the full antennavoltage can reach the load (not shown). The frequency F_(O) of theresonant circuit is chosen to be approximately equal to the frequency ofthe signal to be received.

To obtain only one resonant-circuit module, all resonant circuits in thelow-resistance conductive strips extending beyond the line 4 may becombined. To do this, the wires of the resonant circuits are twistedtogether and wound on a coil form enclosed in a ferrite pot core. Thenumber of turns is chosen so that the frequency F_(O) is reached.

In radio receivers with one printed-circuit board, the antenna wires 2run along the long edge of the printed-circuit board 1. Some radioreceivers have two printed-circuit boards 1 and 5, of which the printedcircuit board 5, for example, is smaller than the board 1. FIG. 3 showsthe printed-circuit boards 1 and 5 in a perspective view. The wire 2 ofone half of the dipole runs along the edge of the printed-circuit board1, and the wire 2 of the other half runs along the edge of theprinted-circuit board 5. The base of the antenna may be located oneither of the boards. In FIG. 3, it is located on the board 5. The loweredge of the printed-circuit board 1 has a metal sheet 6 attached to itwhich is connected to the wire 2 of the lower half of the dipole and,thus, acts as a capacitive load. Attached between the printed-circuitboards 1 and 5 at the upper edges thereof is a metal sheet 7 which isconnected to a metallized area 8 on the printed-circuit board 5.Connected to the metal sheet 7 and the area 8 is the end of the wire 2of the upper half of the dipole so as to create a capacitive load.Arrangements in which capacitive loads are created only with metalsheets or metallized areas or with a combination different from thatshown are also possible.

In the area of the antenna base, which coincides with the lower edge ofthe printed-circuit board 5 in the example shown, all conductive stripson the printed-circuit board 1 which extend beyond this area have beenopened to block the flow of RF signals. To this end, resistors R (onlyone resistor shown) of low capacitance and inductance have been insertedin the highly resistive conductive strips, and resonant circuits offrequency F_(O) in the low-resistance conductive strips. The resonantcircuits may all be enclosed in one pot core, as described above.

We claim:
 1. In a miniaturized radio receiver with a housing, said receiver including at least one printed circuit board containing a plurality of components interconnected on said board by means of conductive strips, a dipole antenna having first and second wires directed parallel to one edge of said board with said first wire directed from the top of said edge towards the center of said board and said second wire directed from the bottom of said edge towards the center of said board to create a space between said wires near the center of said board to form a dipole antenna with said base of said antenna positioned near the center of said board, the combination therewith of capacitive loads for said wires comprising:first and second conductive areas with said first area connected to said first wire at the top of said edge and positioned transverse to said first wire, with said second area connected to said second wire at the bottom of said edge and positioned transverse to said second wire, with each conductive area directed parallel to a corresponding side of said printed circuit board and spaced therefrom to create a predetermined capacitive value for each of said antenna wires, and means coupled to said conductive strips on said board to effectively open said conductive strips near said base of said dipole to block the flow of RF signals.
 2. The combination according to claim 1, wherein said means includes a low capacitance and a low inductance resistor, inserted in each conductive strip running between highly resistive sources and loads.
 3. The combination according to claim 1, wherein said means includes a resonant circuit inserted in each conductive strip running between low resistance sources and loads.
 4. The combination according to claim 3, wherein each resonant circuit consists of a wire wound on a coil form.
 5. The combination according to claim 2, wherein each resistor has a value of about 100K ohms.
 6. The combination according to claim 3, wherein said resonant circuits are tuned to the frequency of reception of said radio receiver.
 7. In a miniaturized radio receiver with a housing, said receiver including first and second printed circuit boards with said boards having equal length top and bottom edges and spaced apart in a parallel relation with said top and bottom edges aligned with, one of said boards being of a greater length than said other, with both of said boards supporting a plurality of components interconnected by conductive strips, a dipole antenna having first and second wires, with said first wire directed parallel to a side edge of said first board and said second wire directed parallel to a corresponding side edge of said second board to form said dipole antenna with the base of said dipole positioned near the bottom edge of said smaller board, the combination therewith of capacitive loads for said wires comprising:first and second conductive areas with said first area connected to said first wire and directed transverse to the same and parallel to an edge of said first board, with said second conductive area connected to said second wire and directed parallel to an edge of said second board with said areas creating predetermined capacitive values for each of said wires and means coupled to said conductive strips on said boards to effectively open said conductive strips in the vicinity of said antenna base to block the flow of RF signals.
 8. The combination according to claim 7, further including a third conductive area located between the space between said first and second boards and connected to said conductive area associated with said second smaller board, both areas connected with the end of said second wire.
 9. The combination according to claim 7, wherein said means to open said conductive strips includes a low capacitance, low inductance resistor inserted in each conductive strip running between highly resistive sources and loads.
 10. The combination according to claim 7, wherein said means to open said conductive strip includes a low capacitance, low inductance resistor inserted in each conductive strip running between low resistive sources and loads.
 11. A dipole antenna structure for a miniaturized radio received or the like, said receiver of the type having at least one printed circuit board for containing a plurality of components interconnected on said board by means of conductive strips, said board being generally of a rectangular configuration having parallel top and bottom surfaces interconnected by parallel side surfaces, comprising:a first wire directed along a side edge from a top surface towards the center and a second wire directed along said side edge from said bottom surface towards said center, with each wire spaced from said edge at the same distance and directed relatively parallel thereto, with said wires forming a dipole with the base of said dipole positioned near the center of said board and first and second conductive areas each directed parallel to and spaced from an associated top and bottom edge, with the end of said first wire connected to said first area at said top surface and with the end of said second wire connected to said second area at said bottom surface, with said conductive areas creating a predetermined capacitive value for each of said wires and means coupled to said conductive strips on said board to effectively open said conductive strips at the vicinity of said dipole base to block the flow of RF signals. 